diff --git a/Lib/decimal.py b/Lib/decimal.py
index f5277c5..1b11b10 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -1871,6 +1871,7 @@
         """
 
         other = _convert_other(other, raiseit=True)
+        third = _convert_other(third, raiseit=True)
 
         # compute product; raise InvalidOperation if either operand is
         # a signaling NaN or if the product is zero times infinity.
@@ -1900,7 +1901,6 @@
                                        str(int(self._int) * int(other._int)),
                                        self._exp + other._exp)
 
-        third = _convert_other(third, raiseit=True)
         return product.__add__(third, context)
 
     def _power_modulo(self, other, modulo, context=None):
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index e46cd91..96bbafe 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -1970,6 +1970,17 @@
         self.assertRaises(TypeError, c.fma, 2, '3', 4)
         self.assertRaises(TypeError, c.fma, 2, 3, '4')
 
+        # Issue 12079 for Context.fma ...
+        self.assertRaises(TypeError, c.fma,
+                          Decimal('Infinity'), Decimal(0), "not a decimal")
+        self.assertRaises(TypeError, c.fma,
+                          Decimal(1), Decimal('snan'), 1.222)
+        # ... and for Decimal.fma.
+        self.assertRaises(TypeError, Decimal('Infinity').fma,
+                          Decimal(0), "not a decimal")
+        self.assertRaises(TypeError, Decimal(1).fma,
+                          Decimal('snan'), 1.222)
+
     def test_is_finite(self):
         c = Context()
         d = c.is_finite(Decimal(10))